This Klickfix Box fits perfect for the JBL Flip 3. I used Velcro tape to keep the box in place and prevent it from falling out of the box.

In the photos we printed it in two pieces and used screws to attach the Klickfix adapter to the Box.

I have posted both files, with and without the Klickfix adapter so you have the possibility to print it in two different colors and then screw it together :)